The scanty documentation was equally unhelpful, as were my attempts to reverse engineer the flasher with IDA Pro and OllyDbg. Running strings for a clue to some switch or other proved fruitless as well.

UPDATE 1: I finally found the hidden switches in I1100A32.exe with a standard hex editor - they were "encrypted" with a ROT-1 Caesar cipher!! The first group is from the DOS app, the second group from Windows (both versions are included in the EXE, which can be split using DualEXE Manipulator):

I have heard of a /forceit option when executing
the flash. Another option I have seen is /jabil
when forcing it to flash when it thinks it has an
incompatible BIOS update -- maybe try it if the other
option does not work?
Since these batteries are available on eBay for only
$40-50, it is probably not worth the risk of damaging
your system.

Throwing caution to the wind, I decided to give the /forceit option a try (readers: do so at your own risk and joy). Lo and behold, the evil battery check was miraculously bypassed! Hallelujah!